How do I take a flat model and wrap around an axis like a wheel?
One way is to just add an Array modifier to your tread or flat object, bump up the counts a bit and add a new Bezier Circle to the scene.



Then add a Curve modifier, select the correct axis (it sometimes wacks out here, you can just apply transformations before you do this) and tweak accordingly until it aligns properly and is arched around a portion of the curve.



Bump up the array count some more and voila, a tire or whatever object wrapped around a circle. (When doing this, you might have to select the curve and scale it accordingly so that the ends of the object meet. You can also tick 'Merge' in the array modifier or use Alt + C to apply the modifiers and convert everything into one object, after this, if a gap still exists, it can be easily filled.